Proteomics reveals the preliminary physiological states of the spotted seal (Phoca largha) pups

Abstract

Spotted seal (Phoca largha) is a critically endangered pinniped in China and South Korea. The conventional method to protect and maintain the P. largha population is to keep them captive in artificially controlled environments. However, little is known about the physiological differences between wild and captive P. largha. To generate a preliminary protein expression profile for P. largha, whole blood from wild and captive pups were subjected to a label-free comparative proteomic analysis. According to the results, 972 proteins were identified and predicted to perform functions related to various metabolic, immune, and cellular processes. Among the identified proteins, the expression level of 51 were significantly different between wild and captive P. large pups. These differentially expressed proteins were enriched in a wide range of cellular functions, including cytoskeleton, phagocytosis, proteolysis, the regulation of gene expression, and carbohydrate metabolism. The abundances of proteins involved in phagocytosis and ubiquitin-mediated proteolysis were significantly higher in the whole blood of wild P. largha pups than in captive individuals. In addition, heat shock protein 90-beta, were determined as the key protein associated with the differences in the wild and captive P. largha pups due to the most interactions of it with various differentially expressed proteins. Moreover, wild P. largha pups could be more nutritionally stressed and have more powerful immune capacities than captive pups. This study provides the first data on the protein composition of P. largha and provides useful information on the physiological characteristics for research in this species.

Figure 1

Functional distribution of the proteins identified in the whole blood of wild and captive Phoca largha pups based on the GO (a) and KEGG (b) databases.

Figure 2

PLS-DA of proteins in the whole blood from wild and captive Phoca largha pups.

Figure 3

GO terms were significantly enriched (p adjusted by FDR < 0.05, performed by DAVID) in the whole blood of wild and captive Phoca largha pups based on the DEP dataset.

Figure 4

KEGG pathways were significantly enriched (p adjusted by FDR < 0.05, performed by DAVID) in the whole blood of wild and captive Phoca largha pups based on the DEP dataset.

Figure 5

Protein–protein interaction (PPI) networks for differentially-expressed proteins between the whole blood of wild and captive Phoca largha pups. The PPI network had an average node degree of 1.35 and clustering coefficient of 0.491. The PPI enrichment p-value was 0.00532, which indicated that the network had significantly more interactions than expected. The colors of edges specify different types of interaction evidences and the thickness indicates the confidence of data support. STRING (https://string-db.org/) was used to construct the PPI networks of the DEPs to identify the key proteins that changed the physiological functions of P. largha due to captivity.